Women who smoke while they are pregnant often don't admit it, which means they're missing out on an opportunity to get help to kick the habit, new research published in BMJ shows.

Smoking is well-known to increase the risk of premature births and other complications. "What these women are doing inadvertently is not allowing themselves to be guided to available smoking cessation services," Dr. David M. Tappin of the University of Glasgow in Scotland, one of the researchers on the study, told Reuters Health.

In the UK, most women are "booked" into maternity services at eight to 12 weeks of pregnancy. At booking, a midwife interviews the woman, and asks whether or not she smokes. Women who say yes will get a follow-up call to enroll them in a smoking cessation program.

"It's quite an evidence-based, well organized service for them," Tappin noted. "You're not just advising them to stop smoking, you're actually giving them a lot of support to achieve that aim of they want to."

Studies have shown that many women continue smoking while pregnant, especially those living in more deprived areas, Tappin and his colleagues note in their report; in Scotland, 38% of women living in the poorest areas admit to smoking while pregnant, while 8% of those living in the least deprived areas do.

There's evidence that many women who smoke in pregnancy don't admit to it, the researchers add. To investigate how common this might be, Tappin and his team looked at a random sample of roughly 21,000 women in western Scotland who had their blood tested in their second trimester to screen for Down's syndrome and birth defects over a one-year period.

The researchers tested blood samples from 3,475 of these women for cotinine, a nicotine byproduct that remains in the blood for about three days after a person smokes a cigarette, and then compared these results to the answers women had provided at their booking interview when asked if they smoked.

Around 24% of the women had reported being current smokers. But the blood tests revealed that 30% were actually smoking. The women living in the least-deprived areas were the most likely to give a false statement about smoking; 39% of smokers living in these areas didn't admit to it, compared to 22% of the more deprived women.

But given that so many more women smoked during pregnancy in the more deprived areas, Tappin and his colleagues say, there were probably twice as many pregnant smokers going undetected in these areas.

A woman's maternity booking visit is often hectic, and many women may choose not to admit to smoking simply to speed up the process, or because they are ashamed to admit to smoking, Tappin noted.

"There is quite a significant number of women who actually say that they don't smoke because that's the easiest thing for them to do," he said. "They don't want to be seen as bad people by their midwives."

In Glasgow, he added, women undergo carbon monoxide breath tests at their booking visit; these tests can show whether a woman smoked within the past 8 to 10 hours. Even women who told the midwife that they did not smoke are willing to undergo the test, which is usually administered by nursing auxiliaries, not midwives.

"It's really not a hassle and nobody complains about it," he said. And by using this test, Tappin added, it's possible to identify 95% of pregnant smokers, while self-reports will only capture around 75%.

And the women who don't admit to smoking are just as likely to seek help for quitting as those who do admit to it, he added. "I don't think these women who give a false answer are any different from anybody else."

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